Start by heating a large pot over medium heat. Melt the unsalted butter, letting its aroma fill the kitchen. Add the diced onion and sauté until translucent. The colors will brighten up, warning you deliciousness is on the way. Next, add in the garlic, stirring for about a minute. You’ll smell that unmistakable garlic aroma. Add the canned San Marzano tomatoes (juice included) and chicken broth. Stir and bring this concoction to a simmer. Sprinkle in the sugar, balsamic vinegar, oregano, salt, and pepper. Don't forget that pinch of red pepper flakes if you're up for a bit of spice. Let this simmer for 20 minutes.

After simmering, use an immersion blender, or transfer the mixture carefully into a blender. Blend until smooth. For a creamy finish, stir in the heavy whipping cream. The color will shift to a rich, vivid red. Taste and adjust seasonings as needed.

While the soup is simmering, it’s time for that grilled cheese. Heat a skillet over medium-low heat. Spread butter on one side of each slice of brioche. Place the non-buttered side down on the skillet. Layer your cheeses and prosciutto (or bacon if that's your preference) on top. Cover with another slice of bread, butter side up. Cook until golden brown, about 3-4 minutes, before flipping. The key here is patience; too high heat and the bread burns before the cheese melts. Let both sides get that crunchy, golden goodness.

Once both sides are golden and the cheese is melty, remove them from the skillet. Let them cool for a minute before cutting them diagonally. This is absolutely essential; there's just something about a sandwich cut this way.

Now, ladle the creamy tomato soup into bowls. Serve with that delightful grilled cheese alongside.